Solve the problem
PDE: $\quad u_{tt} = 9 u_{xx} , \qquad 0 < x < 1 , \quad t > 0$
BC: $\quad u(0,t) = u(1,t) = 0$
IC: $\quad u(x,0) = 6 \sin( 2 \pi x) , \qquad u_t(x,0) = 8 \sin( 3 \pi x)$

$u(x,t) = {}$

help (formulas)